I don't about the web site, but the TaxCaster smartphone app (android or iOS) includes 2018. The default method looks at your 2017 income and deductions using the 2017 rules, but then there is a tab to review 2018, which gives a summary, and a details button gives you the details. This would also work by using your expected 2018 numbers, ignore the 2017 result, and go straight to 2018.